1. Field of the Invention
The present invention relates to an engine and/or brake control system for use in a vehicle and, more particularly, to such a system incorporating a method or a means effective for in-gear vibration elimination.
2. Description of the Prior Art
An antiskid control is disclosed, for example, in U.S. Pat. No. 3,950,036 issued Apr. 13, 1976 to Fink et al. and in U.S. Pat. No. 3,922,022 issued Nov. 25, 1975 to Ochiai and is provided to prevent the wheels from locking, i.e., from making the skid effect when braking the vehicle. When the vehicle is suddenly braked, the wheels will be locked while the vehicle is still moving. This phenomenon is called a skid. When a skid detector detect the skid, the brake pressure is automatically decreased quickly until the skid is eliminated and, thereafter, the brake pressure is automatically increased bit by bit unless the next skid appears. The retrieve of the brake pressure may cause the wheels to skid for the second time. In such a case, the brake pressure is again decreased and then increased in a similar manner. Thus, when the antiskid control starts, strong and weak braking effects are repeated, resulting in the elimination of the skid effect of the wheels during a high deceleration.
The brake traction control is disclosed, for example, in U.S. Pat. No. 3,608,981 issued Sept. 28, 1971 to Shigetomo is provided to prevent the wheels from making the slip effect when rapidly accelerating the vehicle. When the vehicle starts to move at the full open throttle, the drive wheels may spin. In such a case, the drive wheels are automatically braked to suppress the spin. When the spin is suppressed, the brake is automatically weakened to free the drive wheel. The release of the braking effect may cause the drive wheels to spin again for the second time. In such a case, the brake pressure is again increased to brake the drive wheels. Thus, when the brake traction control starts, the braking effect is given intermittently to the drive wheels, resulting in the elimination of the spin of the drive wheels during a high acceleration.
Since the antiskid control and the brake traction control are both provided for detecting a deviation of the wheel speed with respect to the vehicle speed, the antiskid control and the brake traction control are herein generally referred to as a wheel speed control for controlling the speed of the wheel to become nearly equal to the vehicle speed when the speed of the wheel deviates from the speed of the vehicle.
As apparent from the above, either in the antiskid control or in the brake traction control, an intermittent braking effect is provided at various frequencies depending on the various conditions. When the frequency of the intermittent braking effect synchronizes with the natural frequency of the rocking motion of the engine body, the so-called in-gear vibration will be produced.
The engine is usually mounted on the vehicle chassis through cushions, such as rubber sheets, so that when the vehicle is shaken or when the engine is driven on and off intermittently, the engine body makes a rocking motion about its crankshaft at its natural frequency, about 10 Hz, in a manner indicated by arrows shown in FIG. 1. Thus, when the transmission is set to a particular gear position (referred to as an in-gear position), such a rocking motion of the engine is transmitted, in addition to the engine's original driving force, through the chrankshaft and the clutch mechanism to the drive wheels. The rocking motion applied to the drive wheels are referred to as an in-gear vibration. Therefore, when the in-gear vibration takes place, the vehicle accompanies undesirable vibration in the back and forth direction while moving.
The rocking motion of the engine may be created when the driver intermittently steps down the acceleration pedal, but more often it is created when the antiskid control or brake traction control is effected.
According to one prior art, such as disclosed in Japanese Patent Publication (Examined) No. 60-4020, the in-gear vibration is eliminated as described below.
The antiskid control system operates such that when a wheel speed suddenly decreases quicker than the vehicle speed decreases (i.e., vehicle deceleration), a brake pressure decrease signal is generated to decrease brake pressure aiming to recover the wheel speed up to a desirable speed slightly less than the vehicle speed. But sometimes, this sudden decrease of brake pressure induces in-gear vibration while at other times it does not induce such vibration. If in-gear vibration is induced the wheel speed increases and then decreases much more quickly than in normal wheel speed recovery, and does so in a vibratory manner with a resonance frequency of approximately 10 Hz. A typical antiski control system reacts to these quick increases and decreases of wheel speed by increasing and decreasing brake pressure accordingly. These quick increases and decreases of brake pressure are naturally synchronized with the resonance frequency and amplify the vibration of the wheel speed and the brake pressure, resulting in severe vibration of the vehicle itself.
According to the system disclosed in Japanese Patent Publication No. 60-4020, when another brake pressure decrease signal is generated within a predetermined time, such as 0.2 second, from the first brake pressure decrease signal, such a brake pressure decreases signal will be nullified or ignored upon assumption that the second brake pressure decrease signal generated within 0.2 second is totally caused by the counteraction of the first brake pressure decrease. Thus, the brake pressure will not be decreased repeatedly with an interval less than the predetermined time. This will prevent the engine body from making a rocking motion about its crank shaft, thereby preventing the in-gear vibration.
However, the problem in Japanese Patent Publication No. 60-4020 is such that if the skid really occurs within the predetermined time, such a skid will be ignored. The skid will be detected only after a time lapse of more than 0.2 second and, therefore, the skid will be enhanced. Thus, the skid will not be effectively eliminated.
The same problem will occur in the case of elimination of the in-gear vibration under the brake traction control as carried out by a system similar to the above.